Three gun control advocacy groups are reporting record numbers of contributions and volunteers in the wake of the Dec. 14 shootings at Sandy Hook Elementary School in Newtown, Conn.

While the NRA said Wednesday that its membership is up by half a million members, to 4.5 million, the Brady Campaign to Prevent Gun Violence said that it has raised $5 million in recent weeks, said spokeswoman Debra DeShong Reed.

"We've had support after past tragedies, like Aurora (Colo.) and other mass shootings, but the support and resources that have been coming in lately far surpasses anything we've ever seen," said DeShong Reed.

The amount the Brady Campaign has raised in the past several weeks tops the $2.9 million the group raised in all of 2010, which is the most recent federal record available detailing the charity's contributions. And DeShong said the $5 million is equivalent to their entire budget for 2012.

That said, gun control groups are still far behind gun-rights advocates. The NRA didn't respond to requests about whether it has seen a spike in contributions. But the group had enough in its coffers to spend more than $24 million on federal elections last year.

The only gun control group that came close to the NRA's purse was the Super-PAC Independence USA, funded entirely by New York Mayor Michael Bloomberg. That group spent $8 million on federal elections last year. By contrast, the Brady Campaign, spent $4,000 on the 2012 campaign.

In 2006, Bloomberg founded the group Mayors Against Illegal Guns, a group that says it has also benefited from unprecedented spikes in contributions, especially small dollar contributions via their website. The group wouldn't give exact figures, but director Mark Glaze said the total is "very large," thanks to $5 contributions from Tennessee and $100,000 checks from Chicago.

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"This is not just a few people with means bankrolling a movement, this is a groundswell driven by people who want to feel that their kids are safe," Glaze said. "What we're seeing is exponentially more money and more new members in such a short period of time -- far more than we've ever seen before."

Glaze said the average contribution to the group is $72. And the group now touts 1.2 million supporters, about half of which have signed up since the Newtown, Conn., shootings, Glaze said.

A third gun control group, Coalition to Stop Gun Violence, also reports being inundated with contributions and volunteers, although its executive director Josh Horowitz declined to give totals. He said that, in the days after the shooting, the group had to call in two extra volunteers just to respond and organize the dozens of calls from volunteers wanting to help.

The uptick in contributions is allowing Coalition to Stop Gun Violence, which had 5 full-time employees and 2 part-timers, to hire two more full-time employees, Horowitz said.

"I've been doing this for 23 years and I've never seen anything like it," he said. "Our organization may be small compared to the NRA, but our movement is no longer small compared to the NRA."